Obstructive sleep apnea (OSA) affects approximately 18 to 22 million adults in the United States. As the prevalence of OSA continues to increase with the growing obesity epidemic, so too has our understanding of the far-reaching health consequences of OSA, including an increased risk of hypertension, heart disease, stroke, diabetes, occupational injuries, motor vehicle injuries, and overall mortality. Recently, evidence suggestive of yet another important disease burden associated with OSA has begun to emerge: increased risk of incident cancer and cancer mortality. Given that OSA is a highly treatable condition, such evidence suggests an important opportunity for cancer prevention. Few epidemiologic studies, however, have explored the possible link between OSA and cancer, and no studies, to date, have assessed the impact of OSA treatment on cancer rates. The objective of this project is to evaluate the relationship of obstructive sleep apnea with cancer incidence and survival, placing particular focus on the impact of obstructive sleep apnea severity and treatment on cancer rates. In Aim 1, we will characterize ways in which the severity of OSA, captured in the form of five clinical measurements recorded during diagnostic sleep studies, relates to cancer incidence (1a) and to cancer survival and prognostic tumor characteristics (1b). In Aim 2, we will examine the association of continuous positive airway pressure (CPAP) treatment use for OSA, and CPAP treatment compliance, with cancer incidence (2a) and cancer survival (2b). In pursuit of these Aims, this project efficiently leverages an ongoing linkage between medical records from the University of Washington (UW) Sleep Center and the Surveillance, Epidemiology, and End Results (SEER) cancer registry serving western Washington State. Building on this linkage, detailed medical record review will be conducted on a subset of the >15,000 patients diagnosed with OSA at the UW Sleep Center between 2005-2011, including all such patients diagnosed with cancer after being diagnosed with OSA (N~920) and a subset of OSA patients not diagnosed with cancer (N~720). Through this detailed medical record review and by extracting data from electronic medical records, information will be collected on demographic factors, comorbidities, body mass index, and smoking history, as well as measures of OSA severity collected at the time of OSA diagnosis, and indicators of CPAP use and compliance collected at UW Sleep Center follow-up visits. Information on cancer attributes from the SEER registry, such as tumor site and stage at cancer diagnosis, will facilitate further detailed analyses. This study will mark one of the largest, and the most comprehensive investigation into the relationship between OSA and cancer to date. Informed interventions to improve the diagnosis of OSA and encourage proper OSA treatment could provide an efficient approach to reducing cancer incidence and improving cancer survival. Insights gained through this novel study could thus motivate important opportunities for primary, secondary, and tertiary prevention of cancer morbidity and death through OSA screening and treatment.